Conventionally, illumination apparatuses with a light emitting diode (LED) used as a light source have been prevalently used. For example, Japanese Patent Laying-Open No. 2006-210272 (PTD 1) discloses an illumination apparatus including an LED light source and an LED drive device that turns on the LED light source. PTD 1 describes the illumination apparatus with the LED light source formed of a plurality of LEDs connected in series. The LED light source receives a current controlled to be constant to hold each LED constant in brightness.
Furthermore, in recent years, a number of illumination apparatuses with an organic electroluminescence (EL) panel used as a light source have been proposed. The organic EL panel is a surface emitting device, and accordingly, an illumination apparatus having an organic EL panel with a light emitting surface having a larger area can emit light in a larger amount. Increasing the organic EL panel's substrate in size, however, may result in a production apparatus increased in size, poor yields and other disadvantages. Accordingly, a plurality of organic EL panels of a size allowing the panels to be easily produced are aligned to provide a light emitting surface increased in size. This configuration, as well as the illumination apparatus using the LED light source as described above, has a plurality of organic EL panels connected in series and receiving a prescribed current to ensure constant brightness.
When an illumination apparatus formed of a plurality of light emitting devices connected in series has any light emitting device with a short circuit fault, the portion having the short circuit fault may locally generate heat and thus damage the illumination apparatus. Accordingly, the short circuit fault of the light emitting device must be detected and driving the plurality of light emitting devices must be stopped.
Whether a plurality of light emitting devices have a short circuit fault is detected in the illumination apparatus of PTD 1 via a configuration including a voltage detection unit to detect voltage for each LED group formed of three series-connected ones of the LEDs, and a fault detection unit to detect, based on a value in voltage detected by the voltage detection unit, whether the LED light source is faulty. The fault detection unit calculates each LED group's forward voltage based on the voltage detected by each voltage detection unit. The forward voltage is then compared with a fault detection threshold value, and when the forward voltage is below the threshold value, the fault detection unit determines that the LED group of interest has at least one LED with a short circuit fault.